South Korean President Moon Jae-in on Monday hailed North Korea's decision to permanently shut down its only known nuclear test site later in the month, noting it will mark the start of the process to denuclearize the communist state and also reaffirm Pyongyang's commitment to denuclearization.

"I highly evaluate and welcome North Korea's decision to transparently open the dismantlement of its Punggye-ri nuclear test site to the international community following its release of American captives," Moon said in a weekly meeting with his aides at his office Cheong Wa Dae.

Pyongyang released three U.S. citizens held in the communist state last week in an apparent goodwill gesture ahead of its leader Kim Jong-un's meeting with U.S. President Donald Trump.

The Kim-Trump meeting is set to be held in Singapore on June 12.

North Korea agreed to publicly shut down its nuclear test site in a historic summit between Moon and Kim on April 27 at the border village of Panmunjom inside the Demilitarized Zone that divides the two Koreas. It later said the dismantlement will take place from May 23-25, with journalists from South Korea, the United States, China, Russia and Britain to witness it.

Moon said the shutdown will have a special meaning for three different reasons.

"First, it will have a special meaning as it will be an initial step in the complete denuclearization of North Korea. Second, it could be viewed positively in that North Korea is showing a great commitment to the success of the North-U.S. summit. Third, I wish to highly evaluate the move in that North Korea is sincerely taking steps to implement each and every promise Chairman Kim made to me at the South-North Korea summit," he said, according to Cheong Wa Dae pool reports.

The president said the U.S. too is making sincere efforts to make the upcoming summit a success.

"As the people are witnessing, preparations to successfully hold the North Korea-U.S. summit for complete denuclearization of the Korean Peninsula are soundly underway between the two countries. Our government too is working together," he said.

Moon then called for bipartisan efforts to support the U.S.-North Korea summit.

"It goes far beyond advantages or disadvantages in the local elections. I hope our political circles too will show politics of harmony to the people at least on this issue," he was quoted as saying.

Moon's remarks came as the opposition parties, led by the main opposition Liberty Korea Party, have claimed the ongoing dialogue with North Korea may be aimed at aiding the president's ruling Democratic Party in the upcoming mayoral and gubernatorial elections set to be held one day after the U.S.-North Korea summit.

Turning to domestic issues, the president called for efforts to enhance independence of the human rights watchdog.

"The National Human Rights Commission must be able to independently fulfill its duties without the interference of any powers or political forces," the president said.

To this end, the president said the government will more transparently select the new chief of the human rights commission in the future.

The president also called for efforts to prevent and punish tax evasion attempts, especially by the superrich.

"Evading tax by illegally hiding assets in other countries is a key example of anti-social activity that must be eradicated," he told the meeting.

The call came after the National Tax Service filed a complaint against 39 prominent figures suspected of hiding their wealth or income in other countries, and thus evading tax.

His remarks also came amid possible prosecution probes into tax evasion allegations facing two of the countries' largest conglomerates: LG and Hanjin Group. (Yonhap News)